1. Field of the Invention
The present invention relates to a film deposition apparatus that deposits a thin film on a substrate by supplying a plurality of process gases that react with each other to the substrate in turn.
2. Description of the Related Art
A process is known that alternately supplies a plurality of, for example, two kinds of process gases that react with each other to a substrate such as a semiconductor wafer (which is hereinafter called “wafer”) as a method of depositing a high dielectric film such as hafnium oxide (Hf—O) on the substrate. In this method, a thin film is formed by depositing an atomic layer or a molecular layer on the wafer in a layer-by-layer manner, and the method is called an ALD (Atomic Layer Deposition) method as a generic term. When depositing a hafnium oxide film, a TDMAH (Tetrakis(dimethylamino)hafnium) gas and an ozone (O3) gas are respectively used as a source gas and an oxidation gas, and a film deposition temperature is set at about 250 degrees C. As an apparatus to deposit a high dielectric film by the ALD method, a configuration is known that includes a turntable to rotate a wafer and gas injectors lined up away from each other along a moving path of the wafer on the turntable that are arranged in a vacuum chamber.
Some devices utilizing the high dielectric film are required to contain impurities as little as possible, for example, to reduce a leak current. To achieve this, setting a film deposition temperature high is advisable. However, when the film deposition temperature is set at a decomposition temperature of a source gas or higher, a decomposed matter is attached to an inner wall of a gas injector due to the thermal decomposition of the source gas. This is because an internal pressure of the gas injector is likely to become higher than a pressure of the vacuum chamber. When the decomposed matter is attached to the inner wall of the gas injector, the decomposed matter is likely to cause particles by being released from the inner wall in the middle of the film deposition process. Accordingly, to reduce the amount of particles, maintenance of the gas injector has to be performed frequently. Hence, there is a trade-off between depositing a high-quality high dielectric film and reducing adhesion of the attached decomposed matter within the gas injector, and it is very difficult to reduce the adhesion of the attached decomposed matter while depositing a high-quality thin film.
Japanese Patent No. 3952341 discloses a technique in which a nitrogen gas is supplied from a surface of an injector to reduce a reaction between tin tetrachloride and water vapor on a surface of the injector when a thin film is deposited by using a CVD (Chemical Vapor Deposition) method. Japanese Laid-Open Patent Application Publication No. 2008-508744 and Japanese Laid-Open Patent Application Publication No. 2008-538256 disclose a technique that cools an injector head or an injector. However, these patent documents do not study the thermal decomposition of a source gas when depositing a thin film by the ALD method. Moreover, Japanese Laid-Open Patent Application Publication No. 2011-100956 discloses an example of combining a rectifying member with an apparatus including the above-mentioned turntable, but does not disclose a problem in depositing a high dielectric film.